Varnish, prepreg, film with resin, metal foil-clad laminate, and printed circuit board

ABSTRACT

The invention provides a varnish produced through reaction between a compound having an amino group and a resin having a functional group capable of reacting with an amino group, and having a polycyclic structure, wherein a portion of a plurality of the functional group of the resin is caused to react with the amino group of the compound in a solvent, and also a varnish produced through reaction between a compound having a phenolic hydroxyl group and a resin having a functional group capable of reacting with a phenolic hydroxyl group, and having a polycyclic structure, wherein a portion of a plurality of the functional group of the resin is caused to react with the phenolic hydroxyl group of the compound in the solvent. The invention also provides a prepreg, a resin-coated film, a metal-foil-clad laminate, and a printed wiring board produced by use of any of the varnishes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of pending applicationSer. No. 13/581,009, filed Sep. 19, 2012, the contents of which areincorporated herein by reference in their entirety. Ser. No. 13/581,009is a National Stage Application, filed under 35 USC 371, ofInternational (PCT) Application No. PCT/JP2010/063771, filed Aug. 13,2010.

TECHNICAL FIELD

The present invention relates to a varnish employed for producing, forexample, a laminate or printed wiring board used in electronic devices;to a prepreg produced from the varnish; to a resin-coated film producedfrom the varnish; to a metal-foil-clad laminate produced by use of thevarnish; and to a printed wiring board produced by use of the varnish.

BACKGROUND ART

In recent years, with the progress of small-sized, lightweightelectronic devices, printed wiring boards used for such devices havebeen required to have high-density wiring, which is achieved through,for example, stacking of a large number of thin layers or formation of amicro-wiring pattern. Regarding the realization of high-density wiringin such printed wiring boards, the boards are required to have lowthermal expansion coefficient, for the purpose of improving thereliability of micro-wiring patterns on the boards. Particularly whensuch a wiring board is used as a package substrate, which is ahigh-density printed wiring board on which a semiconductor device suchas a semiconductor chip has been mounted, strict requirements areimposed on the properties of the wiring board, as compared with the caseof, for example, a core substrate.

For mounting of a semiconductor device, a flip-chip bonding process hasbeen widely used, in place of a conventional wire bonding process. Inthe flip-chip bonding process, a wiring board and a semiconductor deviceare connected by means of a solder ball in place of a wire, which isused in the wire bonding process, to thereby mount the device on thewiring board. This mounting process may be applied to semiconductorpackages such as CSP (chip scale package), PoP (package on package), andSiP (system in package).

When an electronic component is connected to a wiring board by means ofsolder balls, the solder balls and the wiring board are heated to about300° C. during solder reflow. Generally, the wiring board is formed of alaminate including a metal foil, and a resin-coated film or a prepregformed from a resin composition and a fibrous substrate or a support,wherein a wiring pattern is formed from the metal foil. Therefore, theremay arise problems in that the wiring board expands due to heat; warpageoccurs in the wiring board due to the difference in thermal expansioncoefficient between the resin forming the wiring board and theelectronic component (in particular, a semiconductor device) mounted onthe wiring board; and stress is concentrated particularly on the solderballs, which connect the semiconductor device and the wiring board,resulting in cracking and connection failure.

Warpage in a semiconductor package having a PoP structure will bespecifically described with reference to FIG. 1. This semiconductorpackage includes a substrate 18 and a wiring board provided thereon viasolder balls 22, wherein the wiring board includes a semiconductorpackage substrate 16 having through-holes 20, a semiconductor chip 10electrically connected to the substrate 16 by means of bonding wires 14,and a sealing material 12 provided on the semiconductor chip 10. Whenheat is applied to the wiring board having this structure, warpageoccurs due to the difference in thermal expansion coefficient betweenthe sealing material 12, the chip 10, and the semiconductor packagesubstrate 16, resulting in cracking C.

Under such a circumstance, demand has arisen for a laminate which isless likely to warp and has low thermal expansion coefficient.Conventionally, laminates are generally produced by stacking a pluralityof prepregs which have been prepared by impregnation of a glass woven ornonwoven fabric with a resin composition containing an epoxy resin as amain component, followed by drying, and providing a metal foil on onesurface or both surfaces of the thus-stacked prepregs, followed byheating and pressurization. Although an epoxy resin is well balanced interms of, for example, insulating property, heat resistance, and cost,the resin exhibits high thermal expansion coefficient. Therefore, asdisclosed in, for example, Patent Document 1, generally, the thermalexpansion coefficient of a resin composition is reduced through additionof an inorganic filler such as silica.

The thermal expansion coefficient of the resin composition can befurther reduced through incorporation of a larger amount of an inorganicfiller. However, when the resin composition is used for producing amulti-layer wiring board or a package substrate, a limitation is imposedon the amount of the inorganic filler incorporated, since the inorganicfiller may cause, for example, moisture absorption, poor insulationreliability, adhesion failure between the resin and a wiring layer, anddeterioration of drillability.

Patent Document 2 or 3 discloses a technique for reducing the thermalexpansion coefficient of a resin composition by increasing the crosslinkdensity and Tg of the resin composition. However, there is a limitationon the maximum crosslink density, since the technique for increasingcrosslink density (i.e., the technique for shortening chains ofcross-linked molecules) may cause problems in terms of reactivity andresin structure.

Meanwhile, Patent Document 4 discloses an effective technique forreducing the thermal expansion coefficient of a resin composition byemploying an epoxy resin having an appropriate molecular weight of asegment between cross-linking points and having a polycyclic structure.However, conventional epoxy resins having a polycyclic structure exhibitlow solubility in a solvent due to crystallization of the polycyclicstructure caused by intermolecular attraction. Therefore, even when theepoxy resin is dissolved in an organic solvent through heating, theresin is recrystallized after having been cooled to ambient temperature.

Patent Document 5 discloses an effective technique for reducing warpageby employing a resin having a polycyclic structure. Patent Document 5describes that a resin having a polycyclic structure is effectivelyemployed as a sealing material. In the case where such a resin isemployed as a sealing material, the resin is not required to be formedinto a varnish, and thus the resin does not cause a problem in terms ofrecrystallization, which would otherwise occur when the resin isdissolved in an organic solvent.

However, in consideration that a resin having a polycyclic structure isused for producing a laminate, the resin must be dissolved in a solventto form a varnish immediately before production of the laminate, since,as described above, the resin is very hard to dissolve in an organicsolvent, and a varnish formed from the resin exhibits poor storagestability at ambient temperature.

Thus, improvement of the storage stability of a resin having apolycyclic structure at ambient temperature is of great industrialsignificance, since a varnish containing the resin exhibits improvedworkability during use thereof.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Application Laid-Open (kokai) No.2004-182851Patent Document 2: Japanese Patent Application Laid-Open (kokai) No.2000-243864Patent Document 3: Japanese Patent Application Laid-Open (kokai) No.2000-114727Patent Document 4: Japanese Patent Application Laid-Open (kokai) No.2007-314782Patent Document 5: Japanese Patent Application Laid-Open (kokai) No.2007-002110

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a varnish exhibitinghigh storage stability at ambient temperature and excellent workabilityduring use thereof. Another object of the present invention is toprovide a prepreg, a resin-coated film, a metal-foil-clad laminate, anda printed wiring board, each of which is produced from the varnish.

Means for Solving the Problems

The present inventors have conducted extensive studies for achieving theaforementioned objects, and as a result have accomplished the presentinvention. The present invention provides the following.

[1] A varnish produced through reaction between a compound having anamino group and a resin having a functional group capable of reactingwith an amino group, and having a polycyclic structure, wherein aportion of a plurality of the functional group of the resin is caused toreact with the amino group of the compound in a solvent.

[2] A varnish according to [1], which is produced through reactionbetween a compound having a phenolic hydroxyl group and a resin having afunctional group capable of reacting with a phenolic hydroxyl group, andhaving a polycyclic structure, wherein a portion of a plurality of thefunctional group of the resin is caused to react with the phenolichydroxyl group of the compound in the solvent.

[3] A varnish according to [1] or [2], wherein the compound having anamino group is any of guanamine, dicyandiamide, and aminotriazinenovolak.

[4] A varnish produced through reaction between a compound having aphenolic hydroxyl group and a resin having a functional group capable ofreacting with a phenolic hydroxyl group, and having a polycyclicstructure, wherein a portion of a plurality of the functional group ofthe rein is caused to react with the phenolic hydroxyl group of thecompound in a solvent.

[5] A varnish according to [2] or [4], wherein the compound having aphenolic hydroxyl group is a phenol novolak resin or a cresol novolakresin.

[6] A varnish according to any of [1] to [5], wherein the resin containsat least one epoxy group serving as the functional group.

[7] A varnish according to any of [1] to [6], wherein the resin has atleast one structure selected from the group consisting of a biphenylstructure, a naphthalene structure, a biphenyl novolak structure, ananthracene structure, and a dihydroanthracene structure.

[8] A varnish containing a resin component having a structurerepresented by the following Formula (1):

(wherein R¹ represents the residue of a compound having an amino group).

[9] A varnish according to [8], wherein the ratio of the molar fractionof the structure represented by formula (1) to the sum of the molarfraction of the structure represented by formula (1) and that of astructure represented by the following Formula (2):

is 40% or less.

[10] A prepreg produced by applying a varnish as recited in any of [1]to [9] to a substrate, and drying the resultant product under heating.

[11] A prepreg according to [10], wherein the substrate is a glass wovenfabric, a glass nonwoven fabric, an aramid woven fabric, or an aramidnonwoven fabric.

[12] A resin-coated film produced by applying a varnish as recited inany of [1] to [9] to a film, and drying the resultant product underheating.

[13] A metal-foil-clad laminate comprising a prepreg as recited in [10]or [11], and a conductor layer provided on at least one surface of theprepreg.

[14] A metal-foil-clad laminate comprising a resin-coated film asrecited in [12], and a conductor layer provided on at least one surfaceof the film.

[15] A printed wiring board produced by forming a wiring pattern on theconductor layer provided on at least one surface of a metal-foil-cladlaminate as recited in [13] or [14].

Effects of the Invention

According to the present invention, there can be provided a varnishexhibiting high storage stability at ambient temperature and excellentworkability during use thereof, as well as a prepreg, a resin-coatedfilm, a metal-foil-clad laminate, and a printed wiring board, each ofwhich is produced from the varnish.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the state of warpage in a semiconductor package having aPoP structure.

FIG. 2 shows a DSC curve obtained in the case where the ratio byequivalent of YX-8800 to dicyandiamide is 1:1.

BEST MODES FOR CARRYING OUT THE INVENTION [1] Varnish:

A first varnish of the present invention is produced through reactionbetween a compound having an amino group and a resin having a functionalgroup capable of reacting with an amino group, and having a polycyclicstructure, wherein at least a portion of a plurality of the functionalgroup is caused to react with the amino group in a solvent.

The first varnish of the present invention is also regarded as a varnishcontaining a resin component having a structure represented by thefollowing formula (1):

In formula (1), R¹ represents the residue of a compound having an aminogroup. The compound having an amino group will be described hereinbelow.

A second varnish of the present invention is produced through reactionbetween a compound having a phenolic hydroxyl group and a resin having afunctional group capable of reacting with a phenolic hydroxyl group, andhaving a polycyclic structure, wherein at least a portion of a pluralityof the functional group is caused to react with the phenolic hydroxylgroup in a solvent. The compound having a phenolic hydroxyl group willbe described hereinbelow.

As used herein, “resin having a functional group capable of reactingwith an amino group, and having a polycyclic structure” or “resin havinga functional group capable of reacting with a phenolic hydroxyl group,and having a polycyclic structure” may be referred to as “resin having apolycyclic structure.”

The first varnish or second varnish of the present invention(hereinafter these varnishes may be collectively referred to simply as“the varnish of the present invention”) is produced by dispersing, in asolvent, a resin having a polycyclic structure and a compound having anamino group or a phenolic hydroxyl group, and causing the resin to reactwith the compound through, for example, heating. Thus, the solubility ofthe resin having a polycyclic structure in the solvent is improved, andthe varnish can be stored for a long period of time. Since an additiveor the like is not required to be incorporated for improving thesolubility of the resin, properties of the resin are less likely to beimpaired; i.e., the resin maintains its properties for a long period oftime.

The varnish of the present invention will next be described in detail.

(Resin Having Polycyclic Structure)

As used herein, the “polycyclic structure” of the resin refers to astructure formed through bonding of aromatic rings via a single bond, ora structure formed through condensation of aromatic rings.

Examples of the structure formed through bonding of aromatic rings via asingle bond include a biphenyl structure, a biphenyl novolak structure,and a terphenyl structure.

Examples of the structure formed through condensation of aromatic ringsinclude a naphthalene structure, a naphthalene novolak structure, ananthracene structure, a dihydroanthracene structure, a phenanthrenestructure, a tetracene structure, a chrysene structure, a triphenylenestructure, a tetraphene structure, a pyrene structure, a picenestructure, and a perylene structure.

The aforementioned structures may be employed singly or in combinationof two or more species. In order to improve properties (e.g., thermalexpansion property and heat resistance) of the laminates, printed wiringboards, mounted boards, etc. produced from the varnish of the presentinvention, the polycyclic structure is preferably a biphenyl structure,a biphenyl novolak structure, a naphthalene structure, a naphthalenenovolak structure, an anthracene structure, a dihydroanthracenestructure, or the like, more preferably a biphenyl structure, a biphenylnovolak structure, a naphthalene structure, an anthracene structure, ora dihydroanthracene structure. Such a structure is preferably employed,since the structure is three-dimensionally fixed, and thus stacking canbe readily carried out.

The resin having a polycyclic structure is preferably a thermosettingresin, from the viewpoints of high fluidity during heating, as well asheat resistance and dimensional stability after curing. Examples of thethermosetting resin include an epoxy resin and a cyanate resin. In orderto achieve high productivity and easy handling, the thermosetting resinis preferably an epoxy resin.

In the case where an epoxy resin is employed, the epoxy group of theresin is a functional group capable of reacting with an amino group or aphenolic hydroxyl group.

From the viewpoint of moldability, the epoxy resin is preferably anaphthalene novolak epoxy resin or a biphenyl novolak epoxy resin.Meanwhile, from the viewpoint of low thermal expansion property, theepoxy resin is preferably a naphthalene epoxy resin, an anthracene epoxyresin, or a dihydroanthracene epoxy resin. These resins may be employedsingly or in combination of two or more species. In order to exert theperformance of such resins, the total amount of the resins employed ispreferably 30 mass % or more, more preferably 50 mass % or more, on thebasis of the entirety of the epoxy resin.

Specific examples of preferred epoxy resins will next be described.

The biphenyl novolak epoxy resin is preferably an epoxy resinrepresented by the following formula (3). The epoxy resin having astructure represented by the following formula (3) is commerciallyavailable as, for example, NC-3000 (product of Nippon Kayaku Co., Ltd.)

In formula (3), each of R⁴ to R⁷, which may be the same as or differentfrom one another, represents hydrogen or an alkyl group, and n is anumber satisfying the following relation: n>0, preferably 1.5≦n≦4.0.

The naphthalene novolak epoxy resin is preferably an epoxy resin havinga structure represented by the following formula (4). The epoxy resinhaving a structure represented by the following formula (4) iscommercially available as, for example, ESN-175 (product of Tohto KaseiCo., Ltd.).

In formula (4), m is a number satisfying the following relation: m>0,preferably 2≦m≦7.

The dihydroanthracene epoxy resin is preferably an epoxy resin having astructure represented by the following formula (5). The epoxy resinhaving a structure represented by the following formula (5) iscommercially available as, for example, YX-8800 (product of Japan EpoxyResin).

In formula (5), each of R⁸ and R⁹, which may be the same as or differentfrom each other, represents an alkyl group having 4 or less carbonatoms; x is an integer from 0 to 4; and y is an integer from 0 to 6.

The anthracene epoxy resin is preferably an epoxy resin having astructure represented by the following formula (6).

In formula (6), R¹⁴ to R¹⁷ have the same meanings as R⁴ to R⁷ in formula(3).

(Compound Having Amino Group)

The compound having an amino group employed in the present invention hasat least one amino group in the molecule. When, for example, “thereactive group equivalent of a compound having an amino group”: “theepoxy equivalent of an epoxy resin having a polycyclic structure” is1:1, the exothermic onset temperature is preferably 60° C. to 200° C.,more preferably 70° C. to 190° C., particularly preferably 80° C. to180° C. When the exothermic onset temperature falls within the aboverange, curing reaction does not proceed rapidly at ambient temperature,and thus the resultant varnish exhibits improved pot life (storagestability).

The exothermic onset temperature may be determined through DSC(differential scanning calorimetry). Specifically, the exothermic onsettemperature may be determined as shown in FIG. 2 (i.e., a rising point(point A) of a DSC curve obtained in the case where the ratio byequivalent of YX-8800 to dicyandiamide is 1:1).

Examples of the compound having an amino group include guanamines suchas benzoguanamine, acetoguanamine, and spiroguanamine; guanamine resinsderived therefrom; dicyandiamide; melamine and melamine resins derivedtherefrom; triethylenetetramine; and aminotriazine novolak resin. Themolecular weight of such a compound is preferably 60 or more, morepreferably 80 or more. When the compound having an amino group has sucha molecular weight, the compound is sufficiently bulky for preventingmolecular alignment and crystallization of a resin having a polycyclicstructure in the case where the compound reacts and bonds with theresin. Several types of compounds having an amino group may be employedin combination. Among the aforementioned compounds, benzoguanamine,dicyandiamide, or aminotriazine novolak resin is preferably employed,from the viewpoints of, for example, thermal expansion property, heatresistance, and reliability after formation of a laminate.

The residue of the compound having an amino group represented by R¹ informula (1) is, for example, the residue of any of the above-exemplifiedresins and compounds.

(Compound Having Phenolic Hydroxyl Group)

The compound having a phenolic hydroxyl group employed in the presentinvention has one or more hydroxyl groups in the molecule. From theviewpoint of cross-linking, more preferably, the compound has two ormore hydroxyl groups in the molecule. Examples of the compound having aphenolic hydroxyl group include naphthalenediol, phenol novolak resin,cresol novolak resin, bisphenol A novolak resin, aminotriazine novolakresin, bismaleimide-containing aminotriazine novolak resin, bisphenol A,and bisphenol F. Of these, phenol novolak resin or cresol novolak resinis preferably employed. No particular limitation is imposed on themolecular weight of such a compound. Several types of such compounds maybe employed in combination.

When “the reactive group equivalent of a compound having a phenolichydroxyl group”: “the epoxy equivalent of an epoxy resin having apolycyclic structure” is 1:1, the exothermic onset temperature ispreferably 60° C. to 200° C., more preferably 70° C. to 190° C.,particularly preferably 80° C. to 180° C. When the exothermic onsettemperature falls within the above range, curing reaction does notproceed rapidly at ambient temperature, and thus the resultant varnishexhibits improved pot life (storage stability).

When a compound having a phenolic hydroxyl group is employed, asdescribed hereinbelow, a curing promoter is employed in combination.

Upon reaction in a solvent, the compound having a phenolic hydroxylgroup may be employed in combination with a compound having an aminogroup. In this case, the amount of the compound having a phenolichydroxyl group is preferably 0.01 to 100 equivalents, more preferably0.03 to 30 equivalents, on the basis of 1 equivalent of the compoundhaving an amino group. When the amount of the compound having a phenolichydroxyl group is 0.05 to 20 equivalents on the basis of 1 equivalent ofthe compound having an amino group, effective reaction can be allowed toproceed between the compound having a phenolic hydroxyl group, thecompound having an amino group, and the thermosetting resin.

When “the reactive group equivalent of a compound having a phenolichydroxyl group and a compound having an amino group”: “the epoxyequivalent of an epoxy resin having a polycyclic structure” is 1:1, theexothermic onset temperature is preferably 60° C. to 200° C., morepreferably 70° C. to 190° C., particularly preferably 80° C. to 180° C.When the exothermic onset temperature falls within the above range,curing reaction does not proceed rapidly at ambient temperature, andthus the resultant varnish exhibits improved pot life (storagestability).

(Resin Component Having Structure Represented by Formula (1))

The resin component employed in the present invention and having astructure represented by formula (1) may be produced through reactionbetween any of the aforementioned epoxy resins having a polycyclicstructure and a compound having an amino group in a solvent.Specifically, the resin component having a structure represented byformula (1) may be produced through reaction between at least a portionof epoxy groups of the epoxy resin and the amino group of theamino-group-having compound.

Examples of the structure represented by formula (1) will next bedescribed.

The resin component produced from a biphenyl novolak epoxy resinrepresented by formula (3) and a compound having an amino group has astructure represented by the following formula (7).

In formula (7), R¹ has the same meaning as defined above in formula (1)(the same shall apply hereinafter); o is a number satisfying thefollowing relation: o>0; and p is a number satisfying the followingrelation: p>0.

The resin component produced from a naphthalene novolak epoxy resinrepresented by formula (4) and a compound having an amino group has astructure represented by the following formula (8).

In formula (8), q is a number satisfying the following relation: q>0,and r is a number satisfying the following relation: r>0.

The resin component produced from a dihydroanthracene epoxy resinrepresented by formula (5) and a compound having an amino group includesone having a structure represented by the following formula (9).

In formula (9), R⁸ and R⁹ have the same meanings as those described informula (5), and x and y have the same meanings as those described informula (5).

In the varnish of the present invention, the ratio of the molar fractionof a structure; i.e., a resin component, represented by formula (1) tothe sum of the molar fraction of the structure represented by formula(1) and that of a structure represented by the following formula (2) ispreferably 40% or less, more preferably 5% to 40%, much more preferably8% to 40%, particularly preferably 10% to 35%.

When the ratio is 40% or less, the compound having an amino group, whichhas been added through modification, prevents molecular alignment andcrystallization of the epoxy resin having a polycyclic structure.Therefore, the resultant varnish exhibits favorable storage stabilitywithout causing recrystallization.

When the ratio exceeds 40%, curing reaction may proceed, andsatisfactory storage stability may fail to be achieved.

In the present invention, regarding the ratio of the compound having anamino group and/or the compound having a phenolic hydroxyl group to theepoxy resin having a polycyclic structure during reaction, the ratio ofthe amino group equivalent of the compound having an amino group and/orthe hydroxyl group equivalent of the compound having a phenolic hydroxylgroup to the epoxy equivalent of the epoxy resin is preferably 0.05 to20, more preferably 0.10 to 10, particularly preferably 0.20 to 5. Whenthe ratio of the reactive group equivalent of such a compound to theepoxy equivalent of the epoxy resin is 0.05 to 20, the effect ofdissolving the epoxy resin having a polycyclic structure is not lowered,and favorable handling is achieved. When the equivalent ratio fallswithin the above range, and the ratio of the molar fraction of thestructure of formula (1) to the sum of the molar fraction of thestructure of formula (1) and that of the structure of formula (2) fallswithin the aforementioned range, the time required for synthesis can beshortened, and storage stability can be improved.

The varnish of the present invention may further contain, in the resincomponent, a structure represented by the following formula (10).

When a structure represented by formula (10) is contained, in the resincomponent, the ratio of the sum of the molar fraction of the structuresof formula (1) and formula (10) to the sum of the molar fraction of thestructures of formula (1), formula (2), and formula (10) is preferably40% or less, more preferably 1% to 40%, much more preferably 5% to 35%,particularly preferably 10% to 30%.

When the ratio is 40% or less, the compound having an amino group, whichhas been added through modification, prevents molecular alignment andcrystallization of the epoxy resin having a polycyclic structure.Therefore, the resultant varnish exhibits favorable storage stabilitywithout causing recrystallization.

When the ratio exceeds 40%, curing reaction may proceed, andsatisfactory storage stability may fail to be achieved.

When the ratio of the epoxy equivalent to the reactive group equivalentof the curing agent is adjusted to 0.8 to 1.2, the resultant varnishexhibits improved properties after curing.

Preferably, a solvent is added for mixing the epoxy resin having apolycyclic structure with the compound having an amino group and/or thecompound having a phenolic hydroxyl group.

No particular limitation is imposed on the solvent employed, so long asit can dissolve a resin composition containing no solvent, thecomposition being produced through reaction between the epoxy resinhaving a polycyclic structure, the compound having an amino group, andthe compound having a phenolic hydroxyl group. Particularly, acetone,methyl ethyl ketone, methyl butyl ketone, toluene, xylene, ethylacetate, N,N-dimethylformamide, N,N-dimethylacetamide, ethanol, ethyleneglycol monomethyl ether, propylene glycol monomethyl ether acetate, etc.are preferably employed, since such a solvent exhibits excellentsolubility. Particularly preferably, propylene glycol monomethyl etheris employed, since it can dissolve a resin having high crystallinity.

No particular limitation is imposed on the amount of such a solventemployed, so long as the solvent can dissolve a resin compositioncontaining no solvent, the composition being produced through reactionbetween the epoxy resin having a polycyclic structure, the compoundhaving an amino group, and the compound having a phenolic hydroxylgroup. The amount of the solvent employed is preferably 5 to 300 partsby mass, more preferably 30 to 200 parts by mass, on the basis of 100parts by mass of the total amount of the resin component producedthrough reaction between the epoxy resin having a polycyclic structure,the compound having an amino group, and the compound having a phenolichydroxyl group. The aforementioned solvents may be employed in anycombination.

In the present invention, the weight average molecular weight of theresin component after reaction is preferably 800 to 4,000, morepreferably 900 to 3,500, much more preferably 950 to 3,000. The weightaverage molecular weight of the compound contained in the varnish may bedetermined through, for example, GPC (gel permeation chromatography byuse of a calibration curve based on standard polystyrene). When theweight average molecular weight of the compound contained in the varnishfalls within the above range, the resin having a polycyclic structureexhibits improved solubility, and the varnish exhibits favorablehandling property without causing precipitation of crystals.

The varnish of the present invention may optionally contain a resin or acuring agent in addition to the aforementioned component. No particularlimitation is imposed on the curing agent employed, so long as itexhibits the effect of curing a thermosetting resin. Examples of thecuring agent include acid anhydrides such as maleic anhydride and maleicanhydride copolymer, and phenolic compounds such as phenol novolak,cresol novolak, and aminotriazine novolak resins. These curing agentsmay be employed singly or in combination of two or more species.

During production of a laminate, a curing promoter may be added to thevarnish of the present invention. Examples of the curing promoterinclude imidazoles and derivatives thereof, tertiary amines, andquaternary ammonium salts.

The varnish of the present invention may optionally contain anadditional component, so long as the effects of the present inventionare not impaired.

Examples of the additional component include flame retardants such asorganic phosphorus flame retardants, organic nitrogen-containingphosphorus compounds, nitrogen compounds, silicone flame retardants, andmetal hydroxides; organic fillers such as silicone powder, nylon powder,and fluorine compound powder; thickeners such as orben and benton;antifoaming agents or leveling agents such as silicone compounds,fluorine-containing compounds, and polymer compounds; adhesion-impartingagents such as imidazole-containing, thiazole-containing,triazole-containing, and silane-containing coupling agents; UVabsorbents such as benzotriazole compounds; antioxidants such ashindered phenol compounds and styrenated phenol compounds;photopolymerization initiators such as benzophenone compounds,benzylketal compounds, and thioxanthone compounds; fluorescentbrightening agents such as stilbene derivatives; and colorants such asphthalocyanine blue, phthalocyanine green, iodine green, disazo yellow,and carbon black.

The varnish of the present invention may contain an inorganic filler oran additive for the purpose of reducing thermal expansion coefficient orimparting flame retardancy, so long as the effects of the presentinvention are not impaired. Examples of the inorganic filler which mayemployed include silica, alumina, aluminum hydroxide, calcium carbonate,clay, talc, silicon nitride, boron nitride, titanium oxide, bariumtitanate, lead titanate, and strontium titanate. In order to prepare ahomogenous material for forming the multi-layer wiring board of thepresent invention and to achieve favorable handling of the material, theamount of such an inorganic filler incorporated is adjusted to 300 partsby mass or less, preferably 200 parts by mass or less, on the basis of100 parts by mass of the total amount of the resin component of thepresent invention containing no solvent.

In the case where the resin having a polycyclic structure is employed inthe present invention, when a large amount of an inorganic filler isincorporated, a particular attention must be paid, since the inorganicfiller may serve as a “crystalline nucleus” for promotion ofcrystallization. Examples of the additive which may be employed includevarious silane coupling agents, curing promoters, and antifoamingagents. In order to maintain properties of the resin composition, theamount of such an additive incorporated is preferably adjusted to 5parts by mass or less, more preferably 3 parts by mass or less, on thebasis of 100 parts by mass of the total amount of the resin componentcontaining no solvent. Uniform dispersion of such an inorganic filler iseffectively carried out by means of, for example, a grinder or ahomogenizer.

In the present invention, reaction between the resin having a polycyclicstructure and the compound having an amino group and/or the compoundhaving a phenolic hydroxyl group is carried out preferably at 80° C. to250° C., more preferably at 85° C. to 245° C., much more preferably at90° C. to 240° C.

The reaction time is preferably 10 minutes to 30 hours, more preferably30 minutes to 20 hours, much more preferably 1 to 15 hours.

When reaction is carried out under these conditions, there can beadjusted the molar fraction of the resin component represented byformula (1) in the varnish, or the molar fraction of the resin componentrepresented by formula (1) and that of the structure represented byformula (9).

The varnish of the present invention can be suitably employed forforming an organic insulating layer upon production of a multi-layerprinted wiring board or a package substrate. The varnish of the presentinvention may be applied to a circuit board for forming an insulatinglayer. However, industrially, the varnish is preferably employed as amaterial for producing a layered sheet such as an adhesive film or aprepreg.

[2] Prepreg, resin-coated film, metal-foil-clad laminate, and printedwiring board:

The resin-coated film of the present invention is produced by applyingthe varnish of the present invention to a support film; evaporating thesolvent contained in the varnish through drying; and forming a resincomposition layer through semi-curing (B-stage). An appropriateprotective film may be provided on the resin composition layer.

Preferably, the state of semi-curing is maintained so that, duringcuring of the varnish, adhesion is secured between the resin compositionlayer and the substrate on which a conductor wiring pattern is formed,or the burying performance (fluidity) of the varnish with respect to thesubstrate having the conductor wiring pattern is secured.

Application of the varnish may be carried out by means of a coatingmachine such as a die coater, a comma coater, a bar coater, a kisscoater, or a roll coater. Such a coating machine is appropriatelyselected depending on the thickness of the resin-coated film. Drying maybe carried out through, for example, heating or hot air blowing.

No particular limitation is imposed on the drying conditions, but dryingis carried out so that the amount of the organic solvent contained inthe resin composition layer is adjusted to generally 10 mass % or less,preferably 5 mass % or less. The drying conditions may vary with theamount of the organic solvent contained in the varnish or the boilingpoint of the organic solvent. The resin composition layer is formed by,for example, drying a varnish having an organic solvent content of 30 to60 mass % at 50 to 150° C. for about 3 to about 10 minutes. Preferably,suitable drying conditions are appropriately determined on the basis ofthe results of simple preliminary experiments.

The thickness of the resin composition layer formed in the resin-coatedfilm is generally equal to or greater than that of the conductor layer.The thickness of the conductor layer formed on the circuit board ispreferably 5 to 70 μm. In order to reduce the weight, thickness, andsize of the printed wiring board, the thickness of the conductor layeris more preferably 3 to 50 μm, most preferably 5 to 30 μm. Therefore,the thickness of the resin composition layer is preferably greater by 5%or more than that of the conductor layer.

Examples of the support film employed in the present invention includefilms formed from a polyolefin such as polyethylene, polypropylene, orpolyvinyl chloride; a polyester such as polyethylene terephthalate(hereinafter may be referred to as “PET”) or polyethylene naphthalate;polycarbonate; and polyimide; release paper; and metal foils such ascopper foil and aluminum foil.

The support film or the below-described protective film may be subjectedto mud treatment, corona treatment, or release treatment.

No particular limitation is imposed on the thickness of the supportfilm, but the thickness is preferably 10 to 150 μm, more preferably 25to 50 μm. A protective film corresponding to the support film may befurther formed on the surface of the resin composition layer to whichthe support film does not adhere.

No particular limitation is imposed on the thickness of the protectivefilm, and the thickness is, for example, 1 to 40 μm. Formation of theprotective film can prevent contamination of the layer with foreignmatter. The resin-coated film may be stored in a rolled form.

When the printed wiring board (multi-layer printed wiring board) of thepresent invention is produced from the resin-coated film of the presentinvention, for example, the resin-coated film is laminated on onesurface or both surfaces of the circuit board by means of a vacuumlaminator.

Examples of the substrate employed for forming the circuit board includea glass epoxy substrate, a metal substrate, a polyester substrate, apolyimide substrate, a BT resin substrate, and a thermosettingpolyphenylene ether substrate.

As used herein, the term “circuit board” refers to a product includingany of the aforementioned substrates and a conductor wiring (circuit)pattern formed on one surface or both surfaces of the substrate. The“circuit board” encompasses a multi-layer printed wiring board formedthrough alternate stacking of conductor layers and resin compositionlayers, wherein a conductor wiring (circuit) pattern is formed on onesurface or both surfaces of the outermost layer of the multi-layerprinted wiring board. The surface of the conductor wiring layer may beroughened in advance through, for example, blackening treatment.

When the conductor layer is formed on at least one surface of theresin-coated film, the resultant product is regarded as ametal-foil-clad laminate.

In the case where the resin-coated film has a protective film, in theaforementioned lamination process, after removal of the protective film,optionally, the resin-coated film and the circuit board arepreliminarily heated, and the resin-coated film is press-bonded to thecircuit board under pressurization and heating. In the presentinvention, preferably, the resin-coated film is laminated on the circuitboard under reduced pressure through the vacuum lamination process.

No particular limitation is imposed on the lamination conditions, but,for example, the lamination process is preferably carried out under areduced pressure which is a pressure equal to or lower than air pressure20 mmHg (26.7 hPa) under the following conditions: press-bondingtemperature (lamination temperature) of preferably 70 to 140° C., andpress-bonding pressure of preferably 0.1 to 1.1 MPa. The laminationprocess may be of a batch type or a continuous type by means of aroller.

In the case where the resin-coated film is laminated on the circuitboard, and then the support film is removed after cooling to around roomtemperature, the resin composition layer can be formed on the circuitboard through thermal curing after removal of the film. The thermalcuring conditions may be appropriately determined in consideration of,for example, the type of the resin component contained in the resincomposition, or the amount of the resin component. The thermal curingprocess is preferably carried out at 150° C. to 220° C. for 20 minutesto 180 minutes, more preferably at 160° C. to 200° C. for 30 to 120minutes.

In the case where the support film is not removed before the curingprocess, the support film is removed after formation of the resincomposition layer. Subsequently, via holes or through-holes areoptionally formed in the resin composition layer provided on the circuitboard. Formation of holes may be carried out through any known meanssuch as a drill, a laser, or a plasma, or optionally through combinationof these means. Most generally, formation of holes is carried out bymeans of a laser such as carbon dioxide gas laser or YAG laser.

Subsequently, the conductor layer is formed on the resin compositionlayer through dry plating or wet plating. Dry plating may be carried outthrough any known technique such as vapor deposition, sputtering, or ionplating. When wet plating is carried out, firstly, the surface of theabove-cured resin composition layer is roughened with an oxidizing agentsuch as a permanganate salt (e.g., potassium permanganate or sodiumpermanganate), a dichromate salt, ozone, hydrogen peroxide/sulfuricacid, or nitric acid, to thereby form uneven anchors. The oxidizingagent employed is particularly preferably an aqueous sodium hydroxidesolution of, for example, potassium permanganate or sodium permanganate(alkaline aqueous permanganate solution). Next, the conductor layer isformed through combination of electroless plating and electroplating.Alternatively, the conductor layer may be formed only throughelectroless plating by use of a plating resist having a pattern reverseto that of the conductor layer. The subsequent conductor wiringformation process may be carried out through any known technique such asthe subtractive method or the semi-additive method.

The prepreg of the present invention is produced by impregnating afibrous sheet-like reinforcing substrate with the varnish of the presentinvention through the solvent method, followed by heating to theB-stage. That is, the prepreg can be produced through impregnation of afibrous sheet-like reinforcing substrate with the varnish of the presentinvention.

The fibrous sheet-like reinforcing substrate may be, for example, anywell-known one employed for various laminates for electric insulatingmaterial. Examples of the material of the reinforcing substrate includeinorganic fibers such as E glass fiber, D glass fiber, S glass fiber,and Q glass fiber; organic fibers such as polyimide fiber, polyesterfiber, and polytetrafluoroethylene fiber; and mixtures thereof.

Such a substrate is in the form of, for example, woven fabric, nonwovenfabric, roving, chopped strand mat, or surfacing mat. The material orshape of the substrate is determined in consideration of the intendeduse or performance of the resultant product. Optionally, a singlematerial and shape may be employed, or two or more materials and shapesmay be employed in combination. No particular limitation is imposed onthe thickness of the substrate employed, and the thickness may be, forexample, about 0.03 to about 0.5 mm. Preferably, the substrate issubjected to surface treatment with, for example, a silane couplingagent, or subjected to mechanical opening treatment, from the viewpointsof heat resistance, moisture resistance, and processability.

In the solvent method, the sheet-like reinforcing substrate is immersedin the varnish of the present invention, and the sheet-like reinforcingsubstrate is impregnated with the varnish, followed by drying.

Subsequently, the multi-layer printed wiring board is produced from theabove-produced prepreg as follows. For example, a single prepreg of thepresent invention, or optionally a plurality of prepregs of the presentinvention are stacked on the circuit board, and the resultant product issandwiched between metal plates via release films, followed by pressingunder pressurized and heating conditions. Pressurization and heating arepreferably carried out at 0.5 to 4 MPa and 120 to 200° C. for 20 to 100minutes. Similar to the case of the resin-coated film, the prepreg maybe laminated on the circuit board through the vacuum lamination process,and then curing may be carried out under heating. Thereafter, thesurface of the thus-cured prepreg may be roughened in a manner similarto that described above, and then the conductor layer may be formedthrough plating, to thereby produce the multi-layer printed wiringboard.

EXAMPLES

The present invention will next be described in detail by way ofexamples, which should not be construed as limiting the inventionthereto.

Example 1

200 g of a dihydroanthracene epoxy resin (trade name: YX-8800, productof Japan Epoxy Resin, epoxy equivalent: 174 to 183), 13.8 g ofbenzoguanamine (product of Nippon Shokubai Co., Ltd.) serving as acompound having an amino group, 13.2 g of a cresol novolak resin (tradename: KA-1165, product of DIC Corporation, hydroxyl group equivalent:119) serving as a compound having a phenolic hydroxyl group, and 170.2 gof propylene glycol monomethyl ether acetate (product of Kanto ChemicalCo., Inc.) serving as a solvent were added to a four-neck separableflask equipped with a thermometer, a cooling tube, and a stirrer, andthe resultant mixture was stirred under heating at 140° C. Afterconfirmation that the materials were dissolved in the solvent, heatingwas further carried out for 10 minutes, and then 1 g of the resultantvarnish was sampled. The weight average molecular weight of the varnishbefore reaction as reduced to polystyrene was determined throughhigh-performance liquid chromatography (column: TSK-gel G-3000H, productof Tosoh Corporation). Subsequently, reaction was allowed to proceed at140° C. for five hours, and then 1 g of the resultant varnish wassampled. The weight average molecular weight of the varnish as reducedto polystyrene was determined through high-performance liquidchromatography. Thereafter, 92.0 g of the cresol novolak resin (tradename: KA-1165, product of DIC Corporation) was added and dissolved underheating at 100° C. for 30 minutes, to thereby produce a varnish.

The thus-produced varnish was sampled in a volume of 1 mL. Afterconfirmation that particles having a size of 5 μm or more were absent inthe varnish by means of a particle gauge, the varnish was stored at 5°C., and the varnish was visually observed for determining the timeelapsed until precipitation of the materials in the varnish. Whenprecipitation of the materials was observed, 1 mL of the varnish wassampled, and the presence or absence of particles having a size of 5 μmor more was determined by means of a particle gauge. The time elapseduntil confirmation of the presence of particles having a size of 5 μm ormore was regarded as the “storage time” of the varnish.

Example 2

The procedure of Example 1 was repeated, except that the amount ofbenzoguanamine (product of Nippon Shokubai Co., Ltd.) was changed to27.6 g; the amount of the cresol novolak resin (trade name: KA-1165,product of DIC Corporation) was changed to 22.6 g; the amount ofpropylene glycol monomethyl ether acetate (product of Kanto ChemicalCo., Inc.) was changed to 162.8 g; and the amount of the cresol novolakresin (trade name: KA-1165, product of DIC Corporation) added afterreaction was changed to 56.3 g, to thereby produce a varnish. Thestorage time of the varnish was determined.

Example 3

The procedure of Example 1 was repeated, except that 4.6 g of melamine(product of Kanto Chemical Co., Inc.) was employed as a compound havingan amino group; the amount of the cresol novolak resin (trade name:KA-1165, product of DIC Corporation) serving as a compound having aphenolic hydroxyl group was changed to 26.2 g; the amount of propyleneglycol monomethyl ether acetate (product of Kanto Chemical Co., Inc.)was changed to 172.2 g; and the amount of the cresol novolak resin(trade name: KA-1165, product of DIC Corporation) added after reactionwas changed to 46.0 g, to thereby produce a varnish. The storage time ofthe varnish was determined.

Example 4

The procedure of Example 1 was repeated, except that 11.6 g ofdicyandiamide (product of Kanto Chemical Co., Inc.) was employed as acompound having an amino group; the amount of propylene glycolmonomethyl ether acetate (product of Kanto Chemical Co., Inc.) servingas a solvent was changed to 118.8 g; the amount of the cresol novolakresin (trade name: KA-1165, product of DIC Corporation) added afterreaction was changed to 65.8 g; and the reaction time at 140° C. waschanged to three hours, to thereby produce a varnish. The storage timeof the varnish was determined.

Example 5

The procedure of Example 1 was repeated, except that 2.4 g ofdicyandiamide (product of Kanto Chemical Co., Inc.) was employed; theamount of the cresol novolak resin (trade name: KA-1165, product of DICCorporation) was changed to 26.2 g; the amount of propylene glycolmonomethyl ether acetate (product of Kanto Chemical Co., Inc.) waschanged to 137.4 g; and the amount of the cresol novolak resin (tradename: KA-1165, product of DIC Corporation) added after reaction waschanged to 46.0 g, to thereby produce a varnish. The storage time of thevarnish was determined.

Example 6

The procedure of Example 1 was repeated, except that 200 g of anaphthalene novolak epoxy resin (trade name: ESN-175, product of TohtoKasei Co., Ltd., epoxy equivalent: 254) was employed; 3.3 g ofdicyandiamide (product of Kanto Chemical Co., Inc.) was employed; 24.8 gof a phenol novolak resin (trade name: TD-2090, product of DICCorporation, hydroxyl group equivalent: 105) was employed as a compoundhaving a phenolic hydroxyl group; the amount of propylene glycolmonomethyl ether acetate (product of Kanto Chemical Co., Inc.) waschanged to 115.5 g; the amount of the phenol novolak resin (trade name:TD-2090, product of DIC Corporation) added after reaction was changed to41.3 g; and the reaction time at 140° C. was changed to three hours, tothereby produce a varnish. The storage time of the varnish wasdetermined.

Example 7

The procedure of Example 1 was repeated, except that 76.8 g of abiphenyl novolak epoxy resin (trade name: NC-3000-H, product of NipponKayaku Co., Ltd., epoxy equivalent: 284 to 294) was employed in additionto the dihydroanthracene epoxy resin; 62.6 g of aminotriazine novolak(trade name: LA3018-50P, product of DIC Corporation, 50% solution) wasemployed as a compound having an amino group; the amount of the cresolnovolak resin (trade name: KA-1165, product of DIC Corporation) servingas a compound having a phenolic hydroxyl group was changed to 14.8 g;the amount of propylene glycol monomethyl ether acetate (product ofKanto Chemical Co., Inc.) was changed to 230.5 g; the amount of thecresol novolak resin (trade name: KA-1165, product of DIC Corporation)added after reaction was changed to 124.9 g; the reaction temperaturewas changed to 120° C.; and the retention time was changed to 14 hours,to thereby produce a varnish. The storage time of the varnish wasdetermined.

Example 8

The procedure of Example 1 was repeated, except that 76.8 g of abiphenyl novolak epoxy resin (trade name: NC-3000-H, product of NipponKayaku Co., Ltd., epoxy equivalent: 284 to 294) was employed in additionto the dihydroanthracene epoxy resin; 3.8 g of dicyandiamide (product ofKanto Chemical Co., Inc.) was employed as a compound having an aminogroup; the amount of the cresol novolak resin (trade name: KA-1165,product of DIC Corporation) serving as a compound having a phenolichydroxyl group was changed to 18.1 g; the amount of propylene glycolmonomethyl ether acetate (product of Kanto Chemical Co., Inc.) waschanged to 113.0 g; the amount of the cresol novolak resin (trade name:KA-1165, product of DIC Corporation) added after reaction was changed to124.9 g; and the amount of propylene glycol monomethyl ether acetate(product of Kanto Chemical Co., Inc.) added after reaction was changedto 115.1 g, to thereby produce a varnish. The storage time of thevarnish was determined.

Example 9

The procedure of Example 1 was repeated, except that 200.5 g of abiphenyl novolak epoxy resin (trade name: NC-3000-H, product of NipponKayaku Co., Ltd., epoxy equivalent: 284 to 294) was employed in additionto the dihydroanthracene epoxy resin; 3.9 g of dicyandiamide (product ofKanto Chemical Co., Inc.) was employed as a compound having an aminogroup; the amount of the cresol novolak resin (trade name: KA-1165,product of DIC Corporation) serving as a compound having a phenolichydroxyl group was changed to 197.2 g; the amount of propylene glycolmonomethyl ether acetate (product of Kanto Chemical Co., Inc.) waschanged to 161.6 g; and 164.7 g of propylene glycol monomethyl etheracetate (product of Kanto Chemical Co., Inc.) was added after reaction,to thereby produce a varnish. The storage time of the varnish wasdetermined.

Comparative Example 1

200 g of a dihydroanthracene epoxy resin (trade name: YX-8800, productof Japan Epoxy Resin), 13.8 g of benzoguanamine (product of NipponShokubai Co., Ltd.) serving as a compound having an amino group, 105.2 gof a cresol novolak resin (trade name: KA-1165, product of DICCorporation) serving as a compound having a phenolic hydroxyl group, and170.2 g of propylene glycol monomethyl ether acetate (product of KantoChemical Co., Inc.) serving as a solvent were added to a four-neckseparable flask equipped with a thermometer, a cooling tube, and astirrer, and the resultant mixture was stirred under heating at 140° C.,to thereby produce a varnish.

The thus-produced varnish was sampled in a volume of 1 mL. Afterconfirmation that particles having a size of 5 μm or more were absent inthe varnish by means of a particle gauge, the varnish was stored at 5°C., and the varnish was visually observed for determining the timeelapsed until precipitation of the materials in the varnish. Whenprecipitation of the materials was observed, 1 mL of the varnish wassampled, and the presence or absence of particles having a size of 5 μmor more was determined by means of a particle gauge. The time elapseduntil confirmation of the presence of particles having a size of 5 μm ormore was regarded as the “storage time” of the varnish.

Comparative Example 2

The procedure of Comparative Example 1 was repeated, except that theamount of benzoguanamine (product of Nippon Shokubai Co., Ltd.) waschanged to 27.6 g; the amount of the cresol novolak resin (trade name:KA-1165, product of DIC Corporation) was changed to 78.9 g; and theamount of propylene glycol monomethyl ether acetate (product of KantoChemical Co., Inc.) was changed to 162.8 g, to thereby produce avarnish. The storage time of the varnish was determined.

Comparative Example 3

The procedure of Comparative Example 1 was repeated, except that 4.6 gof melamine (product of Kanto Chemical Co., Inc.) was employed as acompound having an amino group; the amount of the cresol novolak resin(trade name: KA-1165, product of DIC Corporation) was changed to 72.2 g;and the amount of propylene glycol monomethyl ether acetate (product ofKanto Chemical Co., Inc.) was changed to 172.2 g, to thereby produce avarnish. The storage time of the varnish was determined.

Comparative Example 4

The procedure of Comparative Example 1 was repeated, except that 11.6 gof dicyandiamide (product of Kanto Chemical Co., Inc.) was employed; theamount of the cresol novolak resin (trade name: KA-1165, product of DICCorporation) was changed to 65.8 g; and the amount of propylene glycolmonomethyl ether acetate (product of Kanto Chemical Co., Inc.) servingas a solvent was changed to 118.8 g, to thereby produce a varnish. Thestorage time of the varnish was determined.

Comparative Example 5

The procedure of Comparative Example 1 was repeated, except that 2.4 gof dicyandiamide (product of Kanto Chemical Co., Inc.) was employed as acompound having an amino group; the amount of the cresol novolak resin(trade name: KA-1165, product of DIC Corporation) was changed to 72.2 g;and the amount of propylene glycol monomethyl ether acetate (product ofKanto Chemical Co., Inc.) was changed to 137.4 g, to thereby produce avarnish. The storage time of the varnish was determined.

Comparative Example 6

The procedure of Comparative Example 1 was repeated, except that 200 gof a naphthalene novolak epoxy resin (trade name: ESN-175, product ofTohto Kasei Co., Ltd.) was employed; 3.3 g of dicyandiamide (product ofKanto Chemical Co., Inc.) was employed as a compound having an aminogroup; 65.0 g of a phenol novolak resin (trade name: TD-2090, product ofDIC Corporation) was employed as a compound having a phenolic hydroxylgroup; and the amount of propylene glycol monomethyl ether acetate(product of Kanto Chemical Co., Inc.) was changed to 115.5 g, to therebyproduce a varnish. The storage time of the varnish was determined.

Comparative Example 7

The procedure of Comparative Example 1 was repeated, except that 76.8 gof a biphenyl novolak epoxy resin (trade name: NC-3000-H, product ofNippon Kayaku Co., Ltd., epoxy equivalent: 284 to 294) was employed inaddition to the dihydroanthracene epoxy resin; 62.6 g of aminotriazinenovolak (trade name: LA3018-50P, product of DIC Corporation, 50%solution) was employed as a compound having an amino group; the amountof the cresol novolak resin (trade name: KA-1165, product of DICCorporation) serving as a compound having a phenolic hydroxyl group waschanged to 139.7 g; and the amount of propylene glycol monomethyl etheracetate (product of Kanto Chemical Co., Inc.) was changed to 230.5 g, tothereby produce a varnish. The storage time of the varnish wasdetermined.

Comparative Example 8

The procedure of Comparative Example 1 was repeated, except that 76.8 gof a biphenyl novolak epoxy resin (trade name: NC-3000-H, product ofNippon Kayaku Co., Ltd., epoxy equivalent: 284 to 294) was employed inaddition to the dihydroanthracene epoxy resin; 3.8 g of dicyandiamide(product of Kanto Chemical Co., Inc.) was employed as a compound havingan amino group; the amount of the cresol novolak resin (trade name:KA-1165, product of DIC Corporation) serving as a compound having aphenolic hydroxyl group was changed to 143.0 g; and the amount ofpropylene glycol monomethyl ether acetate (product of Kanto ChemicalCo., Inc.) was changed to 228.1 g, to thereby produce a varnish. Thestorage time of the varnish was determined.

Comparative Example 9

The procedure of Comparative Example 1 was repeated, except that 200.5 gof a biphenyl novolak epoxy resin (trade name: NC-3000-H, product ofNippon Kayaku Co., Ltd., epoxy equivalent: 284 to 294) was employed inaddition to the dihydroanthracene epoxy resin; 3.9 g of dicyandiamide(product of Kanto Chemical Co., Inc.) was employed as a compound havingan amino group; the amount of the cresol novolak resin (trade name:KA-1165, product of DIC Corporation) serving as a compound having aphenolic hydroxyl group was changed to 197.2 g; and the amount ofpropylene glycol monomethyl ether acetate (product of Kanto ChemicalCo., Inc.) was changed to 326.3 g, to thereby produce a varnish. Thestorage time of the varnish was determined.

Table 1 shows the weight average molecular weights of the varnishesproduced in the Examples, and the results of measurement of the storagetimes of the varnishes. Table 2 shows the results of measurement of thestorage times of the varnishes produced in the Comparative Examples.

TABLE 1 Product Component Material name name Unit Ex. 1 Ex. 2 Ex. 3 Ex.4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Epoxy Dihydroanthracene YX-8800 g 200.0200.0 200.0 200.0 200.0 200 200 200 resin epoxy resin NaphthaleneESN-175 g 200.0 novolak epoxy resin Biphenyl NC-3000-H g 76.8 76.8 200.5novolak epoxy resin Curing Benzoguanamine — g 13.8 27.6 agent Melamine —g 4.6 Dicyandiamide — g 11.6 2.4 3.3 3.8 3.9 Aminotriazine LA-3018 g62.6 novolak resin Cresol novolak resin KA-1165 g 13.2 22.6 26.2 26.214.8 18.1 197.2 Cresol novolak resin KA-1165 g 92.0 56.3 46.0 65.8 46.0124.9 124.9 after reaction Phenol novolak resin TD-2090 g 24.8 Phenolnovolak resin TD-2090 g 41.3 after reaction Solvent Propylene glycol — g170.2 162.8 172.2 118.8 137.4 115.5 230.5 113.0 161.6 monomethyl etheracetate Propylene glycol monomethyl 115.1 164.7 ether acetate afterreaction Weight average Before reaction 638 645 566 612 570 598 490 6321916 molecular weight After reaction 1122 1318 912 824 982 1093 1023 9753536 Storage time Hrs >168 >168 >168 >168 >168 >168 >168 >168 >168

TABLE 2 Product Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp.Component Material name name Unit Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6Ex. 7 Ex. 8 Ex. 9 Epoxy Dihydroanthracene YX-8800 g 200.0 200.0 200.0200.0 200.0 200 200 200 resin epoxy resin Naphthalene ESN-175 g 200.0novolak epoxy resin Biphenyl NC-3000-H g 76.8 76.8 200.5 novolak epoxyresin Curing Benzoguanamine — g 13.8 27.6 agent Melamine — g 4.6Dicyandiamide — g 11.6 2.4 3.3 3.8 3.9 Aminotriazine LA-3018 g 62.6novolak resin Cresol KA-1165 g 105.2 78.9 72.2 65.8 72.2 139.7 143.0197.2 novolak resin Phenol TD-2090 g 65.0 novolak resin SolventPropylene glycol — g 170.2 162.8 172.2 118.8 137.4 115.5 230.5 228.1326.3 monomethyl ether acetate Storage time Hrs 2 2 3 2 5 3 5 3 12

As shown in Table 1, the storage time of each of the varnishes ofExamples 1 to 6 is 168 hours or longer; i.e., one week or longer. Incontrast, as shown in Table 2, the storage time of each of the varnishesof Comparative Examples 1 to 6 is as short as 2 to 5 hours. The epoxyresin having a polycyclic structure employed in each of the Examples andthe Comparative Examples is called “crystalline epoxy resin,” and theepoxy resin exhibits low solubility in a solvent. Therefore, even in thecase where the varnish is melted by heating to a temperature equal to orhigher than the melting point of the epoxy resin, when the varnish iscooled to room temperature, the resin precipitates in the varnish withina short period of time. In contrast, in the cases of Examples 1 to 6, aportion of a plurality of the functional group of the epoxy resin iscaused to react with the amino group or hydroxyl group of the curingagent, whereby, even when the resultant varnish is stored at 5° C., thestorage time of the varnish becomes 30 times or more that of thevarnishes of the Comparative Examples. Thus, reaction between a portionof a plurality of the functional group of the epoxy resin having apolycyclic structure and the amino group or hydroxyl group of the curingagent is important for securing the storage time of the varnish. Unlikethe case of a conventional varnish, each of the varnishes of theExamples exhibits improved solubility and high stability. In addition,the varnish can be stored for a long period of time; i.e., the varnishexhibits excellent workability and high storage stability.

When a copper-clad laminate is produced from each of the varnishes ofthe Examples, the laminate exhibits low thermal expansion coefficient.Therefore, when a printed wiring board is produced from the laminate,the wiring board can be prevented from occurrence of warpage, whichposes problems in a conventional printed wiring board.

DESCRIPTION OF REFERENCE NUMERALS

-   -   10: Semiconductor chip    -   12: Sealing material (semiconductor package)    -   14: Bonding wire    -   16: Semiconductor package substrate    -   18: Substrate    -   20: Through-hole    -   22: Solder ball    -   C: Cracking caused by warpage

1. A varnish produced through reaction between a compound having anamino group and a resin having a plurality of epoxy groups, and having apolycyclic structure, wherein a portion of the plurality of the epoxygroups of the resin is caused to react with the amino group of thecompound in a solvent, wherein the reaction forms a reaction product,and wherein the reaction product has a weight average molecular weightin the range of 800 to
 4000. 2. The varnish according to claim 1, whichis produced through reaction between the compound having the amino groupand said resin, and between a compound having a phenolic hydroxyl groupand said resin, wherein another portion of the plurality of the epoxygroups of the resin is caused to react with the phenolic hydroxyl groupof the compound in the solvent.
 3. The varnish according to claim 1,wherein the compound having an amino group is any of guanamine,dicyandiamide, and aminotriazine novolak.
 4. A varnish produced throughreaction between a compound having a phenolic hydroxyl group and a resinhaving a plurality of epoxy groups, and having a polycyclic structure,wherein a portion of the plurality of the epoxy groups of the resin iscaused to react with the phenolic hydroxyl group of the compound in asolvent, wherein the reaction forms a reaction product, and wherein thereaction product has a weight average molecular weight in the range of800 to
 4000. 5. The varnish according to claim 2, wherein the compoundhaving a phenolic hydroxyl group is a phenol novolak resin or a cresolnovolak resin.
 6. The varnish according to claim 1, wherein the resinhas at least one structure selected from the group consisting of abiphenyl structure, a naphthalene structure, a biphenyl novolakstructure, an anthracene structure, and a dihydroanthracene structure.7. The varnish according to claim 1, the varnish containing a resincomponent having a structure represented by the following formula (1):

wherein R¹ represents the residue of a compound having an amino group.8. The varnish according to claim 7, wherein the ratio of the molarfraction of the structure represented by formula (1) to the sum of themolar fraction of the structure represented by formula (1) and that of astructure represented by the following formula (2):

is 40% or less.
 9. A prepreg produced by applying, to a substrate, avarnish as recited in claim 1, and drying the resultant product underheating.
 10. A prepreg according to claim 9, wherein the substrate is aglass woven fabric, a glass nonwoven fabric, an aramid woven fabric, oran aramid nonwoven fabric.
 11. A resin-coated film produced by applying,to a film, a varnish as recited in claim 1, and drying the resultantproduct under heating.
 12. A metal-foil-clad laminate comprising aprepreg as recited in claim 9 and a conductor layer provided on at leastone surface of the prepreg.
 13. A metal-foil-clad laminate comprising aresin-coated film as recited in claim 11, and a conductor layer providedon at least one surface of the film.
 14. A printed wiring board producedby forming a wiring pattern on the conductor layer provided on at leastone surface of a metal-foil-clad laminate as recited in claim
 12. 15.The varnish according to claim 4, wherein the compound having a phenolichydroxyl group is a phenol novolak resin or a cresol novolak resin. 16.The varnish according to claim 4, wherein the resin has at least onestructure selected from the group consisting of a biphenyl structure, anaphthalene structure, a biphenyl novolak structure, an anthracenestructure, and a dihydroanthracene structure.
 17. A prepreg produced byapplying, to a substrate, a varnish as recited in claim 4, and dryingthe resultant product under heating.
 18. A resin-coated film produced byapplying, to a film, a varnish as recited in claim 4, and drying theresultant product under heating.
 19. A prepreg produced by applying, toa substrate, a varnish as recited in claim 7, and drying the resultantproduct under heating.
 20. A resin-coated film produced by applying, toa film, a varnish as recited in claim 7, and drying the resultantproduct under heating.
 21. The varnish according to claim 1, wherein theresin has at least one structure selected from the group consisting of abiphenyl structure, a biphenyl novolak structure, a naphthalenestructure, a naphthalene novolak structure, an anthracene structure, anda dihydroanthracene structure.
 22. The varnish according to claim 4,wherein the resin has at least one structure selected from the groupconsisting of a biphenyl structure, a biphenyl novolak structure, anaphthalene structure, a naphthalene novolak structure, an anthracenestructure, and a dihydroanthracene structure.
 23. The varnish accordingto claim 1, which further includes a solvent for said reaction product.24. The varnish according to claim 4, which further includes a solventfor said reaction product.